Charge-transporting thin-films made of organic compounds are used as emissive layers and charge injection layers in organic EL devices. In particular, a hole injection layer is responsible for transferring charge between an anode and a hole transport layer or an emissive layer, and thus serves an important function in achieving low-voltage driving and high brightness in organic EL devices.
Processes for forming the hole injection layer are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. Comparing these different processes, wet processes are more capable of efficiently producing thin-films having a high flatness over a large surface area. Hence, with the progress currently underway toward organic EL displays of larger surface area, there exists a desire for hole injection layers that can be formed by wet processes.
In view of these circumstances, the inventors have developed charge-transporting materials which can be employed in various wet processes and which, when used in hole injection layers for organic EL devices, are capable of achieving excellent EL device characteristics. The inventors have also developed compounds of good solubility in organic solvents for use in such charge-transporting materials (see, for example, Patent Documents 1 to 4).